Abstract Prospective cohort studies in individuals at risk for Type 1 diabetes (T1D) have established that diagnosis of the disease occurs at a late stage in the progressive decline in ?-cell function, when the majority of ?-cell function has been lost and the possibility for disease prevention is gone. Current measures of autoantibodies, HLA typing, and oral glucose tolerance tests (OGTT) are able to identify persons with up to an 80% five-year risk of developing the disease. Thus, new biomarkers are urgently needed to improve early risk characterization and to monitor the autoimmune disease process before the complete destruction of ?-cells. Our long-term goal is to develop new sensitive and specific markers for early accurate prediction of diabetes and to develop strategies by which to screen populations to identify individuals at risk. MicroRNAs (miRNAs) are a recently discovered class of evolutionarily conserved small noncoding RNAs that negatively regulate the expression of protein-coding genes. Recent studies from our lab and others have indicated that miRNAs control immune cell development/function and are involved in cytokine-mediated ?-cell apoptosis. Furthermore, more than 20% of miRNAs are located in human or mouse diabetes Idd loci and there are different expression profiles of miRNAs in the immune cells during T1D development and in ?- cells during their apoptosis, suggesting the potential involvement of miRNAs in T1D development. More recently, it has been discovered that serum/plasma contain large amount of stable miRNAs, deriving from various tissues/organs. This exciting discovery has opened the possibility that cell-free circulating miRNAs could represent a surrogate of miRNA expression in diseased tissues and serve as disease biomarkers. Using miRNA arrays, we recently identified distinct serum miRNA biomarkers related to immune cells and ?-cells for diabetes staging in the nonobese diabetic (NOD) mice and defined specific miRNA expression profiles in 28 diabetes families. The objective here is to identify and confirm specific serum miRNA biomarkers for early T1D prediction. Our preliminary findings lead to our central hypothesis that miRNAs derived from islets and immune cells during T1D development could be detected in the serum and serve a novel class of blood-based biomarkers for T1D prediction. We will test our hypothesis by two Specific Aims. In Aim 1, we will further identify and confirm serum miRNA biomarkers for T1D using T1DGC samples. In Aim 2, we will identify and evaluate serum miRNA biomarkers for T1D prediction using DPT-1 samples. The results from the proposed pioneering studies may enable us to define new stable serum biomarkers, miRNAs, to predict T1D development, and may also facilitate the development of new intervention strategies for T1D therapy.